Tungsten filament fabrication



Sept. 8, 1964 A. F. MOORE ETAL TUNGSTEN FILAMENT FABRICATION 2 Sheets-Sheet 1 Filed Oct. 16. 1961 mll INVENTORS lg I ORIUEY A/PTHUI? E MOORE JUST/M J. HULL P 3, 1964 A. F. MOORE ETAL 3,148,267

. TUNGSTEN FILAMENT FABRICATION Filed Oct 16, 1961 2 Sheets-Sheet 2 ARTi-mRJF. MOORE JUST TORS AT RNEY 3,143,267 TUNGSTEN FELAMENT FAEKHCATEQN Arthur F. hioore, Top-afield, and Justin 5. Hull, Ipswich, lllass, assignors to Sylvania Eleehic Products, line, a corporation of Delaware Filed 6st. 16, 1% Ser. No. 145,400 4 Claims. (63!. 219-153) This invention relates to lamp filaments and more particularly to lamp filaments for use in tubular incandescent lamps.

Tubular lamps having high luminous efiiciency and long life, such as iodine-quartz lamps, have found many practical applications throughout the lighting industry. These lamps exhibit their long life and high luminous efiiciency because of a regenerative getter action occuring within the envelope during operation, in which tungsten iodide is produced when iodine contained within a fill gas combines chemically with particles of tungsten evaporating from the incandescing filament. Subsequent thermal decomposition of the tungsten iodide returns the tungsten particles to the filament to start the cycle anew. In conventional incandescent lamps, that is those not utilizing a fill gas containing iodine, the tungsten particles will evaporate and deposit on the relatively cold envelope wall, thus causing a reduction of luminous etliciency of the lamp due to blackening. Furthermore, when large amounts of particles evaporate from any one point on the filament, a rupturing may occur. in either case, the lamp will have to be replaced.

In the past, methods have been devised for the fabrication of the iodine-quartz lamp and procedures have been developed for the fabrication of the tungsten filament. An example of a method for fabricating the lamp and introducing iodine into the envelope is described in the copending United States patent application of Audesse, entilted Method for lntrducing iodine Into a Lamp Envelope, Serial No. 102,480, filed April 12, 1961, now Patent No. 3,063,778, and assigned to the same assignee as instant application. In the method described by Audes'se and in most methods of fabricating a quartziodine lamp, it is necessary to seal a supported, axially positioned, tungsten filament through both ends of an elongated, tubular, high silica content glass envelope. Because of the nature of the regenerative-getter reaction and the ultimate use of the lamp, it is quite important to position the filament axially within the envelope. Due to the nature or" the filament preparation methods and the shape of the filament however, such precise positioning was previously very difiicult to achieve.

When fixtures are constructed for a lamp, they generally include a supporting structure and a reflector designed for a particular shape and type lamp. Not only are the reflectors designed to house the lamp, but also they are designed to reflect the maximum amount of light. Thus, since the shape of the reflector is standard for all lamps of a given type, the positioning and structure of all components of the lamp may not vary appreciably from one lamp to another. For example, the compact shape and high luminous efiiciency of an iodine quartz lamp lends itself quite readily to photographic lighting equipment. For many years, amateur and professional motion picture photographers have been hampered in their endeavors because of the necessity of using a rather cumbersome light-bar housing a plurality of bulky incandescent lamps. The compact iodine-quartz lamp can be adapted to this use and suitable reflectors and supporting structures can be designed. But for the application of the iodine quartz lamp to photographic lighting, rigid spacing requirements have been established. Not only is the distance from the lamp envelope to the reflector a prime consideration, but also the distance from 3,ld8,2fi7 Fatented Sept. 8, 1964 the filament to the reflector is a major factor. Uniformity in filament positioning from lamp to lamp has to be established so that reproducible light output can always be obtained.

The filament previously used in a quartz-iodine lamp had a coiled-coil construction in which the support legs extended on a plane substantially parallel to the axis of the scond coil of the filament. inordinate care had to be exercised by an operator in sealing the filament within the envelope because of the requirement for coaxial positioning. The support legs of prior art filaments did not readily lend themselves to such positioning.

It was then discovered that if the support legs of the filament are shaped into coaxial alignment with the axis of the second coil, that uniformly positioned metal to glass seals can easily be made in the envelope. But since the coiled-coil tungsten filament had already been fabricared, such shaping operations are quite diflicult to achieve, particularly because a very thin and easily breakable filament is being worked upon.

In particular, the filament worked upon is quite breakable beoause it has been recrystallized. Normally drawn tungsten wire is in the form of long strand-like fibers, but afiter anealing, relatively small crystals are formed which are easily broken upon bending. Thus, not only must correct support be given to the wire, but also heating within precise limits is vital since the tensile strength of the stabilized or recrystallized wire is materially reduced.

The most widely accepted method of fabricating this type coiled-coil filament is to form a first coil by wrapping a length of tungsten filament wire, usually 0.005 to 0.016 inch in diameter, about a molybdenum mandrel, usually 0.020 to 0.040 inch in diameter. When the desired length of the first coil has been formed, the mandrel and wire is rolled into a reel and anealed in a furnace with a hydrogen atmosphere to set the shape. The anealed coil and mandrel are then wound about a retractable pin to form a second coil and then severed into desired lengths. After stabilization of the shape of the second coil by heating it in a furnace containing a hydrogen atmosphere, a coiled-coil tungsten filament wrapped about a mandrel is formed.

When practicing the principles of our invention and working upon a filament, the mandrel may either be removed or not as desired. When such removal is desired, the entire coiled-coil filament is treated in an acid bath to dissolve the mandrel according to conventional .proce dures. Our coaxial aligning method is performed upon the supporting legs of the coiled-coil tungsten filament, that is either the longitudinal extensions of the second coil of the filament containing the mandrel or short tungsten rods extending from within the bore of the first coil of a mandrel-less filament. According to our invention, the support legs are aligned with the axis of the second coil either before the acid treatment, if it is desired to shape the filament itself, or after the acid treatment if it is desired to shape the metal support rods.

In both alternatives, during shaping, at least the outermost windings of the second coil are firmly, but carefully retained and the entire filament made part of an electrical circuit. A forming tool adapted to conduct electricity, is moved towards a portion of the support leg to be shaped and at the moment of contact an electrical circuit is made and heating of the filament commences. The heating and forward movement of the forming tool is continued until the portion of the support leg is aligned with the axis of the second coil of the filament. Care must be exercised in heating the filament because if the temperature is too high, the metal will tend to oxidize, but if insufiicient heating occurs, the coil may break since it is quite brittle. Generally, the coil should be heated from 300 to 1000 C. The entire operation may be per- 3 formed upon one support leg at a time or, if desired, it may be performed on both legs simultaneously. In any event, irrespective of whether the filament itself has been shaped or whether the inserted rods have been shaped, a permanent, coaxially aligiment of the filament supports with the axis of the second coil can be obtained.

Accordingly, the primary object of our invention is the coaxial positioning of the filament supports of a coiled-coil filament;

An another object of our invention is the production of a coiled-coil filament having filament supports extending coaxially with the axis of the second coil.

A feature of our invention is that the support legs of the filament are coaxially positioned while the coil is heated, thereby eliminating the possibility that the legs might break during shaping and further ensuring a rather permanent set in the shape.

Many other advantages, features, and objects will become manifest to those conversant with the art, upon making reference to the detailed description which follows and the accompanying sheets of drawings in which preferred equipment and methods for coaxially aligning supportlegs of coiled-coil tungsten filaments are shown and described, and wherein the principles of the instant invention are incorporated by way of illustrative example.

The figures of the drawings are in the nature of flow sheets, showing the steps and tools used to perform our invention. In each of the figures, similar numerical designations are indicative of similar elements. Of these drawings, FIGURES 1 through 6 refer to the species of our invention wherein an end of the mandrel-containing filament is to be shaped and FIGURES 7 to 12 refer to the species wherein a support rod extending from the bore in a mandrel-less filaments is to be shaped.

FIGURE 1 is an elevational view of a coiled-coil tung sten filament wrapped about a mandrel (not shown) and having support legs extending on a plane with the periphery'of the second coil.

FIGURES 2a and 2b are cross sectional and top planar views respectively of a retainer and tools which may be used to position coaxially a support leg of a coiled-coil filament.

FIGURE 3 is a cross sectional view of similar equipment as illustrated in FIGURE 2. In this figure however, the relative positioning of the forming tools has been changed and electrical contact has just been made with the filament, thereby commencing heating.

FIGURE 4 is similar to the cross sectional views of the previous figures but herein, the support leg has been aligned with the axis of the second coil of the filament through the movement of the forming tools.

In FIGURE 5, the forming tools have been retracted to their original position and the heating of the filament has been discontinued. The filament is ready for removal from'the retainer.

The elevational view shownin FIGURE 6 illustrates the filament as shown in FIGURE 1, after coaxial alignment of one of the filament support legs.

FIGURE 7 is an elevational view of another type of filament which may be shaped according to our invention. The coiled-coil filament illustrated herein has had the mandrel removed and short metal rods have been inserted within the bore of the first coil of the filament.

FIGURES 8a and 8b are cross sectional and top planar views respectively of I equipment for coaxially Shaping metal rods which are inserted Within the first coil of the filament to act as support legs. The filament is shown positioned within a retainer and a support leg is positioned with a jig. Poised over the jig is a shaping tool electrically connected to the retainer so that upon contact of the shaping tool with the filament, current will pass through the filament, thus heating it by resistance heating.

In FIGURE 9, the electrical contact between the shaping tool and the support leg has just been made and heating has commenced.

Shown in FIGURE 10 is the shaping tool at its lowest position and the shaping of the filament support leg has just been performed.

In FIGURE 11, the shaping tool has been retracted from the jig and the coaxially aligned filament is ready for removal from the retainer.

FIGURE 12 shows the ultimate shape after one of the support legs has been shaped into coaxial alignment with the axis of the second coiled-coil filament.

Referring now to the first sheet of drawings, in FIGURE 1 the coiled-coil filament 6 comprises a first coil 1 which is prepared from filamentary material tightly wound about a mandrel (not shown) and a second coil 2 which is prepared of windings of the first coil 1. At each end of the filament 6, support legs 16 and 17 extend on a plane with the periphery of the second coil 2. Particularly, when fabricating the coiled-coil filament for use in the method to be described with reference to the first sheet of drawings, the first coil 1 is made by winding tungsten wire usually of 0.005 to 0.016 inch in diameter about a molybdenum mandrel usually 0.020 to 0.040 inch in diameter. The mandrel is retained within the first winding of the coil, but not shown in the drawing because of the tightness of the coil. The second coil 2 is thenmade by wrapping the first coil 21 containing the mandrel about a retractable pin (not shown) usually of 0.040 to 0.080 inch in diameter to form a coiled-coil filament of 0.070 to 0.152 inch outside diameter. Support legs 16 and 17 extend from either end of the second coil 2 as unitary prolongations thereof and are aligned in substantially the same plane as the periphery of the coil. Because light output is dependant upon, among other things, the length of the filament, it is highly desirable to wind first coil l as tightly as possible and the addition of the second coil 2 provides an extra length of filament. Generally, when the first coil It has outside diameter of 0.030 to 0.072 inch, the second coil 2 may be 10 to 30 turns per inch to produce the coiledcoil 6.

In FIGURE 2:: the coiledcoil filament 6 of FIGURE 1 has been inserted within a cavity 5 of a variable sized retainer l. Tightening or loosening turn screw 12 will vary the size of cavity 5 by moving movable side 7 of the retainer 4 toward or away from stationary side 8. The variable size of the cavity is provided so that the filament 6 may be held firmly, but carefully held by at least the upper most winding of the second coil 2 and preferably by all of the windings during coaxial aligning operations.

As shown, preferably the cavity 5 is suificiently deep so that just the support leg which is being worked upon extends from the top. In this manner, a more efficient coaxial alignment will be made.

Connected to convenient points on retainer 4 and shaping tool 18 are electrical lead-in lines 10 and 11 associated with a power source 14 When a bifurcated end 9 (shown in FIGURE 21:) of the shaping tool 18 touches support leg 16 of the filament 6, an electrical circuit will be set up thereby heating the filament 6 and support leg 16 by resistance heating to make it more malleable. To prevent short circuiting, shaping tool 18 is insulated from retainer 4 by an insulator 19.

As shown in FIGURE 25, aligning and support tool 15 is positioned at approximately right angles to bifurcated end 9 of the shaping tool 13. The relative positioning of the two tools I3 and 15 is such that upon forward movement, the support leg 16 of the filament 6 will be moved into alignment with the axis of the second coil 2 of the filament. Thus, the surface of aligning and support tool 15 which contacts the support leg I6 is coincident with the axis with the second coil 2 and preferably is on a plane with the upper surface of the retainer 4', so that it may slide thereover. Shaping tool IS is electrically insulated from both a retainer 4 and aligning tool 15.

and upon full extension of these tools over the cavity 5, the bifurcated end 9 will protrude coincident with the axis of the second coil 23. Preferably, aligning tool 15 is slightly raised from the upper surface of shaping tool 18 so that lateral support may be given during the coaxial aligning operation without setting up a short circuit. It is possible however, to position the aligning tool below the shaping tool 18 so as to provide such support and insulation. But when desired, the two tools may be placed upon the same plane if they are insulated from each other or if they are made part of the same circuit and both are insulated from retainer 4.

As shown in FIGURE 3, the bifurcated end 9 of the shaping tool 18 has just made contact with the support leg 16 of the filament 6 and thus, a circuit has been made and resistance heating commenced. Because of the very thin filament diameter, of the first coil, generally about .030 to .072 inch, the operating temperature of 300 to 1000" C. will be rapidly reached. Temperature control is quite important because extremes in temperature will cause the filament 6 to oxide. But if the temperature is not reasonably high, the metal will be too brittle to be shaped and will tend to snap upon being moved by shaping tool 18.

Simultaneously with the heating and together with the forward movement of shaping tool 13, aligning tool 15 is being moved into position. Generally we prefer the ultimate position of the bifurcated end 9 the shaping tool 18 to be coincident with the axis of the second coil of the filament 6. ligning tool 15 gives lateral support to the rear of the support leg 16 of the filament 6 so that a fairly permanent set can be made while the filament is within the cavity 5. Now it is apparent that equivalent means may be used to provide such lateral support to the support leg 16 and for example, a hinged door having a side coincident with the axis of the cavity might be closed after the filament 6 has been inserted.

As the shaping tool 18 continues its advance, the support leg 16 is carried over by the bifurcated end 9 until a position is reached coincident with the axis of the second coil of the filament 6 as shown in FIGURE 4. By such movement, the coil has been placed in direct contact with an edge of aligning tool 15 and a permanent set in the coil is being made. The heating is continued because the circuit of the power source 14 to the shaping tool 18 and retainer 4- is still being made through the filament 6 and support leg 16.

Promptly after alignment, the shaping tool 1% and the aligning tool 15 are retracted to their original positions as shown in FIGURE 5. Since the bifurcated end 9 is no longer in contact with the support leg 16, which has remained in the coiled position in which it was set, the heating has stopped and the coil is quickly cooled to ambient temperatures. After a retraction of the tools 15 and 18, the filament may be removed from cavity 5 by loosening screw 12, thus loosening movable retainer 7.

Afterwards, the above described operation may be repeated on the other support leg 1'7 of the filament, but if desired the entire operation of shaping both support legs 16 and 17 may be done simultaneously by duplicating the movable equipment shown. But since our operation particularly describes shaping of a single end of the filament 6, we illustrate the coaxial alignment of only one support leg 16 as shown in FIGURE 6. The support leg l6 has been shifted from alignment with the periphery of the second coil 2 to an alignment with its axis. After both of the support legs 16 and 17 have been aligned, the mandrel (not shown) may be removed by acid treatment according to methods well known in the art.

Before a metal to glass seal can be made and the mandrel-less filament enclosed within an envelope, which is generally prepared of a high melting, high silica content glass such as quartz, certain lead-in connections must be made, since the filament itself will not make an efiicient seal. Small rods are inserted within each longitudinally extendin prolongation of the filament. The free ends of the metal rods are spot welded to very thin intermediate foil sections of molybdenum according to conventional techniques. Current lead-in wires are also attached to the molybdenum foil.

Now as we have stated. when the lamp is fabricated it is essential that the coiled-coil filament is axially aligned within the envelope and to this end in another alternative we may coaxially align the tungsten metal rods which act as support legs. Thus, as an alternative to the coaxial alignment performed upon the filament itself as described previously, the coaxial alignment may be performed on the metal rods which have been placed within the bore of the first winding. In this other embodiment of our invention, the metal rods are inserted Within the ends of the coiled-coil filament which has the mandrel already removed by methods well known in the art. Generally, the metal rods may be of substantially the same outside diameter as the mandrel which was removed.

In those cases where it is desired to coaxially align the metal rods rather than the filament itself, the following procedure can be used. FIGURE 7 illustrates a mandrelless, coiled-coil filament 31 with metal rods 32 and 30 inserted Within lateral prolongations 34 and 35 of the second coil 33 which is formed from winding of the first coil 36. As shown, lateral prolongations of the second coil 33 are positioned substantially on a plane substantially parallel to the axis of the second coil 33.

When shaping the metal rods into coaxial alignment with the second coil, 21 filament with the rods extending from the ends is inserted within a cavity 37 of retainer 38 as shown in FIGURES 8a and 8b. The retainer 38 is generally just slightly wider and at least as deep as the outside diameter of the filament 31. When using such dimensions, it is possible to hold the filament rather firmly during the coaxial alignment operation. The support leg of the filament, comprising the extension 34 of the filament and the metal rod 32, rests upon a forward cradle 39 and is suspended over rear cradle 49 and a die Which comprises a shoulder 42 and base 43. The shape of the lower die conforms to the shape of upper movable die 41. The lower die generally has a depth equal to one half the outside diameter of the coiled-coil filament 31 and thus, the bottom is in a plane with the axis of the coiled-coil filament 31. We prefer to extend a groove 49 and 44 along the length of the forward and rear cradles 39 and 49 respectively, on a plane with the axis of the filament 31, so that uniform seating may be always obtained.

In FIGURE 9, upper die 41 is shown poised over the lower die and lead-in lines 46 and 4'7 from a power source 48 are connected to retainer 38 and upper die 41 at convenient locations. Upon contact of upper die 41 with metal rod 32 an electrical circuit is made and the metal rod 32 will immediately start to heat by resistance heating, thereby making it more malleable. Preferably the rod should be heated from 200 to 700 C. Temperatures in excess of that range tend to cause oxidation on the exterior surfaces of the rod While below that range, the rod might tend to snap during shaping.

As the upper die 4-1 continues its downward movement, metal rod 32 is gradually shaped into conformity with the lower die and the distal end is forced into rear cradle 40 for support. The lowermost position of the upper die is shown in FIGURE 10. As shown, the metal rod 32 has been shaped into coaxial alignment with the second coil of the filament 31 and the heating is continuing due to contact.

After shaping as shown in FIGURE 10 is completed, the upper die 41 is withdrawn from the lower die as shown in FIGURE 11. The electrical circuit has been broken and heating is discontinued as the upper die 41 is removed. When the upper die 41 has completed its upward motion, the filament 31 may be removed from the cavity 37.

Although we have described the operation with reference to shaping only one end of the support leg at a time, it is apparent that both ends may be shaped simultaneously by duplicating the equipment. Shaping of one end at a sneeze? time however, has many advantages since the length of the cavity 37 will not be fixed and longer or shorter filaments may be shaped interchangeably on the same equipment.

Now turning to FIGURE 12 it will be seen that a portion of one end of the tungsten metal rod 32 of the support legs is aligned with the axis of the second coil 33 of the filament 31. After repeating the above described operation on the unshaped leg 30, portions of both legs 3t? and 32 will extend on the axis of the filament 31.

It is apparent that changes and modifications may be made within the spirit and scope of the instant invention, but it is our intention however to be limited only by the scope of the appended claims.

As our invention We claim:

1. In the process for fabricating a coiled-coil filament, the steps which comprise: holding a coiled-coil filament in a retainer, said filament having at least one filamentary support leg extending longitudinally substantially in a plane With the axis of the second coil; making the filament part of an electrical circuit; contacting the outer side of the said support leg with a shaping tool and commencing resistance heating within said filament; moving said shaping tool and thus at least an end portion of said support leg toward the axis of said coiled-coil filament while continuing said heating, laterally supporting the interior side of said end portion of said filament When said end portion I lized tungsten filament in a retainer, said filament having at least one filamentary support leg extending longitudinally substantially on a plane with the axis of the second coil; making said filament part of an electrical circuit; contacting the outer side of said filament with a shaping tool connected into said electrical circuit and thus completing the circuit and heating the filament with resistance heating; moving said shaping tool and thus at least an end portion of said support leg toward the axis of said coiled-coil filament while continuing said heating; laterally supporting said end portion of said filament when said end portion is substantially aligned with the axis of said filament; withdrawing said shaping tool, thereby breaking said circuit and discontinuing said heating; removing from the retainer a coiled-coil filament having at least an end portion of the support leg substantially aligned with the axis of the filament.

3. The process according to claim 2 wherein the filament is heated from 300 to 1000 C.

4-. In the process for fabricating a coiled-coil filament, the steps which comprise: holding a coiled-coil recrystallized tungsten filament in a retainer, said filament having at least one support leg containing a mandrel, said support leg comprising a unitary prolongation of said filament extending longitudinally substantially on a plane with the axis of the second coil; making said filament part of an electrical circuit; contacting the outer side of said support leg with a shaping tool and causing current fiow in said filament and thus commencing resistance heating Within said filament; moving said shaping tool and thus at least an end portion of said support leg toward the axis of said coiled-coil filament while continuing said heating; laterally supporting the interior side of said end portion of said filament when said end portion is substantially aligned With the axis of said filament; removing said lateral support and withdrawing said shaping tool and discontinuing said heating; removing from the retainer a coiled-coil filament having at least an end portion of one leg substantially aligned with the axis of the second coil.

References Cited in the file of this patent UNITED STATES PATENTS 1,237,371 Murray Aug. 21, 1917 2,393,718 Stenson et al. Jan. 29, 1946 2,472,778 Quinn et al. June 7, 1949 FOREIGN PATENTS 454,472 Canada Feb. 8, 1949 

1. IN THE PROCESS FOR FABRICATING A COILED-COIL FILAMENT, THE STEPS WHICH COMPRISE: HOLDING A COILED-COIL FILAMENT IN A RETAINER, SAID FILAMENT HAVING AT LEAST ONE FILAMENTARY SUPPORT LEG EXTENDING LONGTIDINALLY SUBSTANTIALLY IN A PLANE WITH THE AXIS OF THE SECOND COIL; MAKING THE FILAMENT PART OF AN ELECTRICAL CIRCUIT; CONTACTING THE OUTER SIDE OF THE SAID SUPPORT LEG WITH A SHAPING TOOL AND COMMENCING RESISTANCE HEATING WITHIN SAID FILAMENT; MOVING SAID SHAPING TOOL AND THUS AT LEAST AN END PORTION OF SAID SUPPORT LEG TOWARD THE AXIS OF SAID COILED-COIL FILAMENT WHILE CONTINUING SAID HEATING, LATERALLY SUPPORTING THE INTERIOR SIDE OF SAID END PORTION OF SAID FILAMENT WHEN SAID END PORTION IS SUBSTANTIALLY ALIGNED WITH THE AXIS OF SAID FILAMENT; WITHDRAWING SAID SHAPING TOOL AND DISCONTINUING SAID HEATING; REMOVING FROM SAID RETAINER A COILED-COIL FILAMENT HAVING AT LEAST AN END PORTION OF ONE LEG SUBSTANTIALLY ALIGNED WITH THE AXIS OF THE SECOND COIL. 